1. Field of the Invention
The present invention relates to an engine unit and a motorcycle equipped therewith.
2. Description of the Related Art
A general motorcycle has been known that, due to its limited mounting space, has an engine crankshaft arranged in a lateral direction of the vehicle body, and has a clutch and a main shaft arranged on an axis parallel to the crankshaft. The clutch is connected to one end of the main shaft and transfers power from the crankshaft to the main shaft. The power transferred to the main shaft is transferred to a counter shaft (an output shaft) that is located opposite and parallel to the main shaft via a gear mission, and is output to the rear wheel via this counter shaft. For example, the power is output to the rear wheel via a drive chain wound around a sprocket attached to one end of the counter shaft. The sprocket is wound by a chain with a gear that rotates the rear wheel and therefore is attached to one end of the counter shaft after an engine unit is mounted on a vehicle with front and rear wheels.
Because the sprocket is attached to the counter shaft as described above after the mounting of an engine unit, the clutch that is incorporated beforehand as the engine unit and is arranged, on the side of one end, coaxially with the main shaft at a short distance from the counter shaft, is attached to an end which is on the side laterally reverse to the end to which the sprocket is attached.
There has also been known a transmission that includes a plurality of clutches in order to permit speedy transmission operations of an automobile (see Japanese Patent Laid-Open No. 58-124851, for example).
In recent years, there has been a demand for mounting a multi-speed transmission provided with a plurality of clutches mounted on a vehicle, on a motorcycle having a limited mounting space. When a multi-speed transmission including a plurality of clutches is mounted on a motorcycle, it is necessary to reduce the size of the transmission itself, and, in addition, due to the structure of the motorcycle on which the transmission is mounted, it is necessary to position the center of gravity approximately centrally in the vehicle width direction together with the mounted engine and create a weight balance that is not biased toward the left or right.
A clutch is comparatively heavy for a member that constitutes the drive transmission system. Consequently, for a multi-speed transmission to be mounted on a conventional motorcycle, there is a demand for positioning a plurality of clutches on both left and right sides of the vehicle body away from each other with respect to a counter shaft and a main shaft that is parallel to the counter shaft, in order to maintain the lateral balance of the transmission itself.
That is to say, there is a demand for making the transmission itself small without increasing the shaft-to-shaft distance in the front-back direction of the vehicle body with respect to the counter shaft in the main shaft, which is achieved by arranging one clutch on an extension of one end on the side where a sprocket is attached in the counter shaft.